In order to successfully reprocess used medical instruments such as forceps, retractors, scissors, speculums, rigid endoscopes, flexible endoscopes etc., it is desirable to remove all biological soil such as blood, fat, tissue fragments etc. from the instrument prior to sterilisation or disinfection. Any residual soil left on the device may be very likely to compromise the sterilisation or disinfection processes, thus placing the next patient exposed to the soiled instruments liable to acquire a nosocomial infection.
Typically most medical instrumentation is reprocessed automatically in washer disinfectors. In the case of most surgical instrumentation, the washer disinfectors used are typically provided with a plurality of spray arms. The instruments are loaded into trays and placed into the washer-disinfector for cleaning.
Water is then introduced into the chamber and pumped through the spray arms at a relatively high pressure to provide a pre-wash. The chamber is drained, and additional water added, and heated to between 50° C. and 60° C. Once heated, a small quantity of detergent is pumped into the chamber, and the resultant solution again pumped at relatively high pressure through the spray arms. Because of the extreme agitation caused by the spray arm, it is necessary to use a detergent with little or no tendency to foam, even when contaminated with protein. Any significant foaming produced during the wash cycle may adversely affect the cleaning efficacy, particularly in and around any joints or hinges present on the instrument as the foam may prevent access to the underlying soil. This effect may be even more pronounced in a lumened device.
Whilst many low foam surfactants are known, and have been successfully used in the automated cleaning of medical instruments, many pose certain challenges.
Firstly, whilst the formulation may be low foaming, the foam may be persistent in a dynamic environment such as found in a washer disinfector, particularly in the newer models which utilise higher pressure pumps to improve cleaning efficacy.
Secondly, the most common means to control foam is the use of non-ionic surfactants, particularly alkyl alkoxylates, by manipulation of the solution cloud point. As is known in the art, heating a solution of a non-ionic surfactant above its cloud point typically destabilises foam, causing it to break up and disperse. One side effect of the control of foaming by the manipulation of the solution cloud point is that a solution above its cloud point can appear milky, which will hinder visual observation of the cleaning process.
Another approach to foam control would be to add foam control agents such as silicone oils or silicone/silica defoaming agents. This approach however can lead to the surfaces of the medical instruments becoming contaminated with the defoamer.
One means of preventing foaming would be to use a surfactant free detergent system. Typically this approach has been used in automated dishwashers, using solid detergent systems based on highly alkaline ingredients such as sodium metasilicate, and alkali metal hydroxides. Whilst highly effective as detergents, particularly for fatty or proteinaceous soils, highly alkaline detergents are not suited for the cleaning of many medical instruments, particularly endoscopes, or instruments fabricated from aluminium, or coated with anodised aluminium, due to materials compatibility issues.
Cleaning solutions with a more neutral pH (for example pH 7 to 9) are more instrument-friendly, but are not very effective if formulated without surfactants, as the surfactant assists in the wetting of surfaces, and the solublisation of soils.
Surprisingly it has been found that surfactant free formulations containing alkanolamines, mineral acids, hydroxycarboxylic acid salts and enzymes, at an essentially neutral pH can produce a cleaning solution that produces little or no foam, whilst effectively removing biological soils.
The use of an alkanolamine in a medical instrument detergent has been previously reported. U.S. Pat. No. 6,562,296 for example teaches the use of a non-enzymatic cleaning solution comprising triethanolamine, various chelating agents and a surfactant (N-acyl glutamate), typically added as a wetting agent.
U.S. Pat. No. 4,243,546, EP0481663 and EP0730024 disclose enzyme-containing cleaning solutions which can enzymatically degrade in particular blood proteins. It is proposed there to use triethanolamine for stabilising the enzymes. Each of the formulations also contains, as essential ingredients, surfactants. In the case of U.S. Pat. No. 4,243,546 and EP 0481663, the surfactants are non-ionic, whereas EP 0730024 contains, as an essential component, an anionic surfactant.
The presence of a surfactant within the formulation has the potential to lead to the generation of nuisance foams that can impede the cleaning of medical instruments. There is therefore a constant need for cleaning formulations that produce zero or low foam, even under conditions of high agitation.